This invention relates to an interior electrochromic rearview mirror for a vehicle. Inside rearview mirrors for vehicles have generally been constructed with planar reflective elements. The use of such planar reflective elements provides for a non-distorted image for viewing by the driver. Recently, non-planar inside rearview mirrors have been sold in the aftermarket for supplementing or replacing the inside rearview mirror that comes with the vehicle. Such non-planar rearview mirrors are designed to provide a greater field of view through the inside mirror so as to help eliminate blindspots and/or provide the driver with the ability to view other vehicle occupants, particularly, small children and pets.
Heretofore, various automatic rearview mirrors for motor vehicles have been devised which automatically change from the full reflectance mode (day) to the partial reflectance mode(s) (night) for glare protection purposes from light emanating from the headlights of vehicles approaching from the rear. An example of such an automatic rearview mirror is an electrochromic mirror. Prior inside electrochromic rearview mirrors have all been generally planar. While non-planar outside electrochromic rearview mirrors have been constructed, inside electrochromic rearview mirrors have had planar constructions due to the significant difficulty in constructing non-planar electrochromic elements. The difficulties in producing a non-planar electrochromic mirror are discussed further below following a brief description of the general construction of such electrochromic devices.
The electrochromic mirrors that are typical of modern day automatic rearview mirrors for motor vehicles are disclosed in U.S. Pat. No. 4,902,108, entitled "Single-Compartment, Self-Erasing, Solution-Phase Electrochromic Devices Solutions for Use Therein, and Uses Thereof", issued Feb. 20, 1990, to H. J. Byker; Canadian Patent No. 1,300,945, entitled "Automatic Rearview Mirror System for Automotive Vehicles", issued May 19, 1992, to J. H. Bechtel et al.; U.S. Pat. No. 5,128,799, entitled "Variable Reflectance Motor Vehicle Mirror", issued Jul. 7, 1992, to H. J. Byker; U.S. Pat. No. 5,202,787, entitled "Electro-Optic Device", issued Apr. 13, 1993, to H. J. Byker et al.; U.S. Pat. No. 5,204,778, entitled "Control System For Automatic Rearview Mirrors", issued Apr. 20, 1993, to J. H. Bechtel; U.S. Pat. No. 5,278,693, entitled "Tinted Solution-Phase Electrochromic Mirrors", issued Jan. 11, 1994, to D. A. Theiste et al.; U.S. Pat. No. 5,280,380, entitled "UV-Stabilized Compositions and Methods", issued Jan. 18, 1994, to H. J. Byker; U.S. Pat. No. 5,282,077, entitled "Variable Reflectance Mirror", issued Jan. 25, 1994, to H. J. Byker; U.S. Pat. No. 5,294,376, entitled "Bipyridinium Salt Solutions", issued Mar. 15, 1994, to H. J. Byker; U.S. Pat. No. 5,336,448, entitled "Electrochromic Devices with Bipyridinium Salt Solutions", issued Aug. 9, 1994, to H. J. Byker; U.S. Pat. No. 5,434,407, entitled "Automatic Rearview Mirror Incorporating Light Pipe", issued Jan. 18, 1995, to F. T. Bauer et al.; U.S. Pat. No. 5,448,397, entitled "Outside Automatic Rearview Mirror for Automotive Vehicles", issued Sep. 5, 1995, to W. L. Tonar; and U.S. Pat. No. 5,451,822, entitled "Electronic Control System", issued Sep. 19, 1995, to J. H. Bechtel et al., each of which patents is assigned to the assignee of the present invention and the disclosures of each of which are hereby incorporated herein by reference.
Such electrochromic mirrors may be utilized in a fully integrated inside/outside rearview mirror system or as an inside or an outside rearview mirror system. In general, in automatic rearview mirrors of the types disclosed in the above referenced U.S. Patents, both the inside and the outside rearview mirrors are comprised of a relatively thin electrochromic medium sandwiched and sealed between two glass elements.
In most cases, when the electrochromic medium (which functions as the media of variable transmittance in the mirrors) is electrically energized, it darkens and begins to absorb light. The more light the electrochromic medium absorbs the darker (or lower in reflectance) the mirror becomes. When the electrical voltage is decreased to zero, the mirror returns to its clear high reflectance state. In general, the electrochrornic medium sandwiched and sealed between the two glass elements is comprised of a solution-phase, self-erasing system of electrochromic materials. Other electrochromic media may be utilized. Those media include an approach wherein a tungsten oxide electrochromric layer is coated on one electrode with a solution containing a redox active material to provide the counter electrode reaction.
When operated automatically, the rearview mirrors of the indicated character generally incorporate light-sensing electronic circuitry which is effective to change the mirrors to the dimmed reflectance modes when headlamp glare is detected, the sandwiched electrochromic medium being activated and the mirror being dimmed in proportion to the amount of glare that is detected. As headlamp glare subsides, the mirror automatically returns to its normal high reflectance state without any action being required on the part of the driver of the vehicle.
The electrochromic medium fills a sealed chamber defined by a transparent front glass element, a peripheral edge seal and a rear mirror element having a reflective layer. Conductive layers are provided on the inside of the front and rear glass elements. The conductive layer on the front glass element is transparent while the conductive layer on the rear glass element may be transparent or may be semi-transparent or opaque and may also have reflective characteristics and function as the reflective layer for the mirror assembly.
The conductive layers on both the front glass element and the rear glass element are connected to electronic circuitry which is effective to electrically energize the electrochromic medium to switch the mirror to nighttime (decreased reflectance modes when glare is detected) and thereafter allow the mirror to return to the daytime (high reflectance mode when the glare subsides) as described in detail in the aforementioned U.S. Patents.
To produce a non-planar electrochromic mirror, a planar glass substrate is heated and bent into the desired shape. Problems arise, however, in electrochromic mirrors due to the presence of two glass elements, which both must be bent into conforming shapes. If the front surface of the rear element does not conform identically to the rear surface of the front glass element, the spacing between the elements will not be uniform. This leads to non-uniform coloration of the electrochromic device in its low reflectance state. Additionally, such variations in curvature between the front and rear elements will introduce substantial image distortion into the reflected image. This problem becomes worse when the reflective layer on the electrochromic device is provided on the rear surface of the rear glass element.
To enable the bending of the glass to be more easily controlled, the glass elements may be made using much thinner glass substrates. Unfortunately, as the thickness is decreased, the individual glass elements become fragile and flexible and remain that way during and after the manufacture of an electrochromic mirror.
It is therefore difficult to produce a commercially desirable non-planar electrochromic mirror that has two thin glass elements because each thin glass element will be much more likely to flex, warp, bow and/or shatter. Properties of a solution-phase electrochromic device, such as coloring and clearing times and optical density when colored, are dependent on the thickness of the electrochromic layer (e.g., the spacing between the two glass elements). Maintaining uniform spacing is necessary to maintain uniform appearance. The spacing between thin glass elements can be easily changed even after device manufacture by applying subtle pressure on one of the glass plates. This creates an undesirable non-uniformity in the appearance of the device.